One typical cause for a time change of the performance of a fuel cell is a morphology change of an electrode catalyst. An electrode for the fuel cell generally has catalyst-supported particles prepared by dispersively supporting a catalyst metal, e.g., platinum, on a carrier, e.g., carbon particles. The morphology change of the electrode catalyst is, for example, agglutination of catalyst metal fine particles dispersively supported on the carrier to reduce the overall surface area of the catalyst metal on the electrode. One proposed method of detecting such a morphology change of the electrode catalyst and its degree determines the effective area of the electrode catalyst based on the cyclic voltammetry characteristic (for example, Patent Literature 1).